The field of this invention is that of thermostats and the invention relates more particularly to a thermally responsive control adapted to be mounted on an apparatus whose temperature is to be monitored for moving control means between control positions in response to selected temperature changes.
Conventional thermostats which are widely used on many different kinds of apparatus typically comprise an electrical switch mounted on one end of a generally cylindrical, electrically insulating base to be moved between positions opening and closing an electrical circuit. A dished thermally responsive snap acting thermostat metal element is positioned in a control location at the opposite end of the insulating base so that it moves from an original dished configuration to an inverted dished configuration with snap action in response to selected temperature changes. A motion transfer pin is axially slidable on the base between the thermostat metal element and the switch for moving the switch between the noted control positions in response to snap-acting movement of the element. In such conventional devices, a cup-shaped metal cap is typically deep-drawn from a relatively strong and rigid metal material such as stainless steel and is provided with an apertured flange extending outwardly from the rim of the cap. The cupped part of the cup is fitted over the opposite end of the cylindrical base part and is deformed or indented so that it grips bosses formed on the outer periphery of the base, thereby to secure the snap acting thermostat metal element in the desired control location on the device base. In that arrangement, the flanges of the cup are used for mounting the device on an object or apparatus whose temperatue is to be monitored and serve to position the snap acting thermostat metal element in close heat-transfer relation to the object for sensing changes in object temperature through the metal cap.
Conventional thermostats of that construction have found wide application both because of their low cost and because of their reliability in use. In that regard, the thermostat structure is adapted to be reliably and accurately assembled to precisely position the snap acting thermostat metal element so that it provides its desired control functions at precisely predetermined temperatures. However, it would be desirable to provide further improvements in the structure of the thermostat to permit additional component and assembly cost savings, particularly if such cost improvements could be accomplished while improving thermostat performance and reliability. In that regard, it has been found that the deep-drawn cap tends to be quite expensive when formed of a high strength material such as stainless steel to permit the cap flange to be used in mounting the thermostat. When the cap is made of stainless steel it also displays thermal conductivity which may limit the thermal response characteristics of the thermostat. Most important, where the cap is deformed to directly engage boss means on the electrically insulating base for locating the thermostat metal element, thermal cycling of the device may limit service life by permitting ultimate loosening of the cap with resulting change in the thermal response characteristics of the device.
It is an object of this invention to provide a novel and improved thermally responsive control device; to provide such an improved control device with a rugged reliable construction adapted for widespread application; and to provide such a device which is characterized by relatively lower component cost, by improved assembly cost, by improved reliability in use, and by improved response to changes in temperature of an object whose temperature is to be monitored.